Dual leucine zipper kinase regulates expression of axon guidance genes in mouse neuronal cells

Gene Expression of Neurogenesis Related to Exercise Intensity in a Cerebral Infarction Rat Model

Regular exercise improves several functions, including cognition, in patients with stroke. However, the effect of regular exercise on neurogenesis related to cognition remains doubtful. We investigated the most effective exercise intensity for functional recovery after stroke using RNA sequencing following regular treadmill exercise. Photothrombotic cerebral infarction was conducted for 10-week-old male Sprague-Dawley rats (n = 36). A Morris water maze (MWM) test was performed before a regular treadmill exercise program (5 days/week, 4 weeks). Rats were randomly divided into four groups: group A (no exercise); group B (low intensity, maximal velocity 18 m/min); group C (moderate intensity, maximal velocity 24 m/min) and group D (high intensity, maximal velocity 30 m/min). After 4 weeks, another MWM test was performed, and all rats were sacrificed. RNA sequencing was performed with ipsilesional hippocampal tissue. On the day after cerebral infarction, no differences in escape latency and velocity were observed among the groups. At 4 weeks after cerebral infarction, the escape latencies in groups B, C, and D were shorter than in group A. The escape latencies in groups B and C were shorter than in group D. The velocity in groups A, B, and C was faster than in group D. Thirty gene symbols related to neurogenesis were detected (p < 0.05, fold change > 1.0, average normalized read count > four times). In the neurotrophin-signaling pathway, the CHK gene was upregulated, and the NF-κB gene was downregulated in the low-intensity group. The CHK and NF-κB genes were both downregulated in the moderate-intensity group. The Raf and IRAK genes were downregulated in the high-intensity group. Western blot analysis showed that NF-κB expression was lowest in the moderate-intensity group, whereas CHK and Raf were elevated, and IRAK was decreased in the high-intensity group. Moderate-intensity exercise may contribute to neuroplasticity. Variation in the expression of neurotrophins in neurogenesis according to exercise intensity may reveal the mechanism of neuroplasticity. Thus, NF-κB is the key neurotrophin for neurogenesis related to exercise intensity.

Deciphering the multifunctional role of dual leucine zipper kinase (DLK) and its therapeutic potential in disease

Dual leucine zipper kinase (DLK, MAP3K12), a serine/threonine protein kinase, plays a key role in neuronal development, as it regulates axon regeneration and degeneration through its downstream kinase. Importantly, DLK is closely related to the pathogenesis of numerous neurodegenerative diseases and the induction of β-cell apoptosis that leads to diabetes. In this review, we summarize the current understanding of DLK function, and then discuss the role of DLK signaling in human diseases. Furthermore, various types of small molecule inhibitors of DLK that have been published so far are described in detail in this paper, providing some strategies for the design of DLK small molecule inhibitors in the future.

Dual Leucine Zipper Kinase Regulates Dscam Expression through a Noncanonical Function of the Cytoplasmic Poly(A)-Binding Protein

Dual leucine zipper kinase (DLK) plays a pivotal role in the development, degeneration, and regeneration of neurons. DLK can regulate gene expression post-transcriptionally, but the underlying mechanism remains poorly understood. The Drosophila DLK, Wallenda (Wnd), regulates the expression of Down syndrome cell adhesion molecule (Dscam) to control presynaptic arbor growth. This regulation is mediated by the 3' untranslated region (3'UTR) of Dscam mRNA, which suggests that RNA binding proteins (RBPs) mediate DLK function. We performed a genome-wide cell-based RNAi screen of RBPs and identified the cytoplasmic poly(A)-binding protein, pAbp, as an RBP that mediates Wnd-induced increase in Dscam expression. Genetic analysis shows that Wnd requires pAbp for promoting presynaptic arbor growth and for enhancing Dscam expression. Our analysis revealed that Dscam mRNAs harbor short poly(A) tails. We identified a region in Dscam 3'UTR that specifically interacts with pAbp. Removing this region significantly reduced Wnd-induced increase in Dscam expression. These suggest that a noncanonical interaction of PABP with the 3'UTR of target transcripts is essential for DLK functions.SIGNIFICANCE STATEMENT The kinase DLK plays key roles in a multitude of neuronal responses, including axon development, neurodegeneration, and nerve injury. Previous studies show that DLK acts via mRNAs to regulate protein synthesis, but how DLK does so is poorly understood. This study demonstrates that DLK regulates the synthesis of Dscam through the poly(A)-binding protein PABP-C. Whereas PABP-C is known as a general translational activator, our study shows that DLK-mediated Dscam expression involves a noncanonical interaction between PABP-C and the Dscam mRNA, which leads to a selective regulation of Dscam translation by PABP-C. Thus, our study provides novel insights into the mechanisms that underlie the function of DLK and regulation of gene expression of PABP-C.

DLK regulates a distinctive transcriptional regeneration program after peripheral nerve injury

Following damage to a peripheral nerve, injury signaling pathways converge in the cell body to generate transcriptional changes that support axon regeneration. Here, we demonstrate that dual leucine zipper kinase (DLK), a central regulator of injury responses including axon regeneration and neuronal apoptosis, is required for the induction of the pro-regenerative transcriptional program in response to peripheral nerve injury. Using a sensory neuron-conditional DLK knockout mouse model, we show a time course for the dependency of gene expression changes on the DLK pathway after sciatic nerve injury. Gene ontology analysis reveals that DLK-dependent gene sets are enriched for specific functional annotations such as ion transport and immune response. A series of comparative analyses shows that the DLK-dependent transcriptional program is distinct from that promoted by the importin-dependent retrograde signaling pathway, while it is partially shared between PNS and CNS injury responses. We suggest that DLK-dependency might provide a selective filter for regeneration-associated genes among the injury-responsive transcriptome.

The Expression of Key Guidance Genes at a Forebrain Axon Turning Point Is Maintained by Distinct Fgfr Isoforms but a Common Downstream Signal Transduction Mechanism

During development the axons of neurons grow toward and locate their synaptic partners to form functional neural circuits. Axons do so by reading a map of guidance cues expressed by surrounding tissues. Guidance cues are expressed at a precise space and time, but how guidance cue expression is regulated, and in a coordinated manner, is poorly understood. Semaphorins (Semas) and Slits are families of molecular ligands that guide axons. We showed previously that fibroblast growth factor (Fgf) signaling maintains sema3a and slit1 forebrain expression in Xenopus laevis, and these two repellents cooperate to guide retinal ganglion cell (RGC) axons away from the mid-diencephalon and on towards the optic tectum. Here, we investigate whether there are common features of the regulatory pathways that control the expression of these two guidance cues at this single axon guidance decision point. We isolated the sema3a proximal promoter and confirmed its responsiveness to Fgf signaling. Through misexpression of truncated Fgf receptors (Fgfrs), we found that sema3a forebrain expression is dependent on Fgfr2-4 but not Fgfr1. This is in contrast to slit1, whose expression we showed previously depends on Fgfr1 but not Fgfr2-4. Using pharmacological inhibitors and misexpression of constitutively active (CA) and dominant negative (DN) signaling intermediates, we find that while distinct Fgfrs regulate these two guidance genes, intracellular signaling downstream of Fgfrs appears to converge along the phosphoinositol 3-kinase (PI3K)-Akt signaling pathway. A common PI3K-Akt signaling pathway may allow for the coordinated expression of guidance cues that cooperate to direct axons at a guidance choice point.

Computer-Aided Multi-Target Management of Emergent Alzheimer's Disease

Alzheimer's disease (AD) represents an enormous global health burden in terms of human suffering and economic cost. AD management requires a shift from the prevailing paradigm targeting pathogenesis to design and develop effective drugs with adequate success in clinical trials. Therefore, it is of interest to report a review on amyloid beta (Aβ) effects and other multi-targets including cholinesterase, NFTs, tau protein and TNF associated with brain cell death to be neuro-protective from AD. It should be noted that these molecules have been generated either by target-based or phenotypic methods. Hence, the use of recent advancements in nanomedicine and other natural compounds screening tools as a feasible alternative for circumventing specific liabilities is realized. We review recent developments in the design and identification of neuro-degenerative compounds against AD generated using current advancements in computational multi-target modeling algorithms reflected by theragnosis (combination of diagnostic tests and therapy) concern.